With the advent of more stringent environmental pollution laws, attention has been given to emissions and fuel spillage from the fuel tank. During operation of a vehicle, consumption of the fuel within the tank creates a vacuum therein which degrades operation of the engine and is suddenly released when the cap on the fuel tank is removed. On the other hand, if a motor vehicle sits in the sun or is in an extremely warm environment, the pressure within the fuel tank soon exceeds atmospheric pressure. When the cap is removed, pressure equalization can result in fuel being expelled from the tank.
Japanese Utility Model Application No. 15228/83, laid open on Nov. 13, 1978, describes a fuel tank cap wherein a cam surface is integrally formed on a lock piece. When a key cylinder is rotated after insertion of a key, the lock piece is moved so that engagement between latch 6 and the spring edge of a tank is released. At the same time, the cam surface allows a cooperating arm to be lowered to release pressure within the tank. In order to remove the cap, however, further rotation of the cap is required.
U.S. Pat. No. 3,938,692 issued to Billy G. Crute on Feb. 17, 1976, shows a pressure-vacuum relief fuel tank cap with a roll-over safety valve. This cap also achieves pressure equalization between the inside and outside of the tank.
A problem with the fuel tank caps of the prior art including the two caps specifically referred to above is that the mechanism for pressure relief is located in line with a lock mechanism, the caps are thick and bulky. Also, removed of the caps first requires rotation of the key to unlock the cap and then rotation of the cap. This is an inconvenient set of movements particularly since a filling station attendant is often working onehanded as his other hand is holding the pump nozzle.